#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netdb.h>

void error_handling(char* message);

int main(int argc, char* argv[])
{
    int i;
    struct hostent* host;
    struct sockaddr_in addr; 

    if(argc != 2)
    {
        printf("Usage : %s <IP> \n", argv[0]);
        exit(1);
    }

    //通过IP获取域名等信息
    memset(&addr, 0, sizeof(addr));
    addr.sin_addr.s_addr = inet_addr(argv[1]);
    host = gethostbyaddr((char*)&addr.sin_addr, 4, AF_INET);//IPv4: 4, IPv6: 16 
    if(!host)
        error_handling("gethost error\n");
    
    //官方域名
    printf("Official name : %s \n", host->h_name);
    //其他域名
    for(i = 0; host->h_aliases[i]; i++)//最后是null
        printf("Aliases %d : %s \n", i + 1, host->h_aliases[i]);
    //地址族信息
    printf("Address type : %s \n", host->h_addrtype == AF_INET ? "AF_INET" : "AF_INET6");
    //IP地址信息
    for(i = 0; host->h_addr_list[i]; i++)//结构体中用char*存储的，需要转换成in_addr结构体指针
        printf("IP addr %d : %s \n", i + 1, inet_ntoa(*(struct in_addr*)host->h_addr_list[i]));

    return 0;
}

void error_handling(char* message)
{
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(-1);
}
